/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.feilong.lib.net.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;

/**
 * CRLFLineReader implements a readLine() method that requires
 * exactly CRLF to terminate an input line.
 * This is required for IMAP, which allows bare CR and LF.
 *
 * @since 3.0
 */
public final class CRLFLineReader extends BufferedReader{

    private static final char LF = '\n';

    private static final char CR = '\r';

    /**
     * Creates a CRLFLineReader that wraps an existing Reader
     * input source.
     * 
     * @param reader
     *            The Reader input source.
     */
    public CRLFLineReader(Reader reader){
        super(reader);
    }

    /**
     * Read a line of text.
     * A line is considered to be terminated by carriage return followed immediately by a linefeed.
     * This contrasts with BufferedReader which also allows other combinations.
     * 
     * @since 3.0
     */
    @Override
    public String readLine() throws IOException{
        StringBuilder sb = new StringBuilder();
        int intch;
        boolean prevWasCR = false;
        synchronized (lock){ // make thread-safe (hopefully!)
            while ((intch = read()) != -1){
                if (prevWasCR && intch == LF){
                    return sb.substring(0, sb.length() - 1);
                }
                if (intch == CR){
                    prevWasCR = true;
                }else{
                    prevWasCR = false;
                }
                sb.append((char) intch);
            }
        }
        String string = sb.toString();
        if (string.length() == 0){ // immediate EOF
            return null;
        }
        return string;
    }
}
